1. Field of the Invention
The present invention relates to a non-obvious zoom lens system and an image-pickup apparatus. More specifically, it relates to a zoom lens system capable of shifting an image by shifting part of a lens in a direction substantially orthogonal to the optical axis and relates to an image-pickup apparatus including the zoom lens system.
2. Description of the Related Art
There is a known recording method for a camera in which the light intensity of an image of an object that is formed on an image-pickup element surface by an image-pickup element using a photoelectric conversion element, such as a charge coupled device (CCD) or a complementary method-oxide semiconductor (CMOS), is converted into an electric output and is recorded.
Recently, the advancement in fine processing technology has lead to the increase in the speed of central processing units (CPUs) and the level of integration of recording media. Accordingly, high-speed processing of large volumes of image data that, in the past, could not have been processed has come possible. Furthermore, for light-receiving elements, increase in the level of integration and reduction of size has been carried out. Thus, the increase in the level of integration has enabled recording of higher spatial-frequency, and reduction in size has enabled a reduction in the overall size of a camera.
However, due to such increase in the level of integration and reduction in size, there is a problem in that the area of the light-receiving surface of each photoelectric conversion element is reduced, and the effect of noise increases as the magnitude of the electric output decreases. To prevent such problem, various measures, such as increasing the intensity of the light reaching the light-receiving elements is increases by employing a large focal ratio for the optical system and disposing lens elements (which are known as a microlens array) immediately before each element, has been taken. The microlens array guides light beams that pass through between adjacent elements but limits the exit pupil position of the lens system. When the exit pupil position of the lens system becomes closer to the light-receiving element, i.e., when the angle to the optical axis of the principal light beam incident on the light-receiving element increases, off-axis light beams emitted at the peripheral areas of the screen form a large angle to the optical axis. As a result, the light beams to not reach the light-receiving elements, and the intensity of light becomes insufficient.
Since the angle of view at the telephoto end in an optical system having large zoom ratio is small, there is a problem in that a very small level of shaking of the optical system generates a great level of shaking of the image.
As a shake-correction method of correcting the shaking of an image caused by the shaking of the optical system, an optical shake-correction system is known.
For an optical shake-correction system, a lens-shift method in which part of a lens system is shifted in a direction orthogonal to the optical axis or a variable apex-angle prism method in which the apex angle of a prism disposed immediately before a lens system is changed are known. However, for the variable apex-angle prism method, there is a problem that the size of the system including a driving system is large since the variable apex-angle prism is disposed on the object side of a first lens unit, which is the largest in the lens system.
The optical system of the lens system method can function as an optical shake-correction system for correcting shaking of an image caused by shaking of a camera by shifting lenses using a driving system by, for example, combing a detecting system for detecting shaking of the camera caused by shaking due to, for example, shutter release, a control system for obtaining, on the basis of a signal output from the detecting system, a correction value that is to be applied to the lens position, and a shift-driving system for driving the shifting of a lens on the basis of the output from the control system.
As the above-described lens shift method, for example, methods described in Japanese Unexamined Patent Application Publication Nos. 2005-215385, 2005-128186, and 2004-252196 are known.
The zoom lens system described in Japanese Unexamined Patent Application Publication No. 2005-215385 includes, in order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power. The zoom lens system is configured in a manner such that, when the lens positions change from the wide-angle end to the telephoto end, the first lens unit moves toward the object, the second lens unit moves toward the image, the third lens unit once moves toward the object and then moves toward the image, and the fourth lens unit once moves toward the object and then moves toward the image. With the zoom lens system, an image is shifted by shifting the entire third lens unit in a direction substantially orthogonal to the optical axis.
The zoom lens system described in Japanese Unexamined Patent Application Publication No. 2005-128186 includes, in order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power. The zoom lens system is configured in a manner such that, when the lens positions change from the wide-angle end to the telephoto end, the first lens unit and the third lens unit are fixed in the optical axis direction, the second lens unit moves toward the image, and the fourth lens unit moves so as to compensate for the displacement in the image plane position caused by the movement of the second lens unit. With the zoom lens system, an image is shifted by shifting the entire third lens unit in a direction substantially orthogonal to the optical axis.
The zoom lens system described in Japanese Unexamined Patent Application Publication No. 2004-252196 includes, in order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having positive refractive power, and a fifth lens unit having positive refractive power. The zoom lens system is configured in a manner such that, when the lens positions change from the wide-angle end to the telephoto end, the first to fourth lens units move so that the distance between the first lens unit and the second lens unit increases, the distance between the second lens unit and the third lens unit decreases, the distance between the third lens unit and the fourth lens unit increases, and the fifth lens unit is fixed in the optical axis direction. The third lens unit includes two subunits. With the zoom lens system, an image is shifted by shifting one of the subunits in a direction substantially orthogonal to the optical axis.